I am not sure why this is labeled as a self insert. I don't see anything SI about it. In fact this would be better served on Fiction the sister site of Fan since there is very little HP references in it.

I hope you continue this. I like stories with intelligent protagonist that don't just fight physically, but actually manipulate stuff on the background.

I'm guessing Sophia has Lymphoma or Leukemia, because all other cancer types with an L are rather easy to remember. On top of that, healing something like Liver cancer in the wizarding world, would probably consist of, cut it out, put a new one in. Now to help or not to help. Maybe gratitude from Regulus, on the other hand, she'd have to change her name to Mary Sue.